The present invention relates to a folding device for sewing a second workpiece onto a first workpiece in an automatic sewing machine.
A folding device for an automatic sewing machine for sewing a second sewing material workpiece onto a first sewing material workpiece is known from German Patent DE 37 09 210 C2 (corresponding to U.S. Pat. No. 4,793,272). The folding device has a support plate for receiving the first workpiece, a sword arranged on a sword carrier to receive the second workpiece, and an outer frame arranged on an outer-frame carrier, the outer frame having bend-over means for folding edge portions of the second workpiece around the sword, the sword being moveable by its sword-carrier between a lower working position on the support plate, and an upper working position above the support plate, and the outer frame being moveable by the outer-frame carrier into a lower working position on the support plate and a position near the upper working position of the sword.
The first sewing material is placed on the support plate, properly marked, before the start of the sewing process, and the second sewing material--for instance a pocket blank--is placed on a so-called "sword". The sword is arranged on a sword support so that, on the one hand, it is swingably moveable in the direction toward or away from the support plate; and, on the other hand, is movable into a retracted position in the horizontal plane starting from a lower working position on the support plate. Furthermore, the folding device also includes an outer frame having bend-over means which are arranged thereon and can be positioned in three different positions of swing. The bend-over means fold the second sewing material around the aforementioned sword in such a manner that at least three edge regions, extending beyond the sword, of the second sewing material which is placed on the sword, are folded downward, i.e. bent over. Thereupon the second sewing material which has been folded around the sword is lowered, together with the sword and the outer frame, onto the first sewing material, the second and first parts being held clamped between the support plate, the outer frame, and the sword.
As a result of this folding process, there is an accumulation of at least four layers of material in the upper region of the second sewing material--for example, in the region of engagement of the pocket which is to be sewn on--and a further accumulation of four layers of material in the lower region. When pockets with rounded edges are sewn on, folds occur in the inner regions (the regions of minimal radius) of the rounded corners, due to the pushing together of the folded edge regions, causing an uncontrollable thickening of the second material at the place in question. Between the upper and lower regions of the folded second material, on the other hand, there are only two layers of material, namely one layer of the first material and another layer of the second material.
The main disadvantage of the known folding device is that the folded second material is dependably clamped only in the region of the maximum accumulation of layers of material--for instance in the region of engagement of the pocket to be sewn on--after the folding process has been carried out, while at all other places within the folded edge regions, the folded edge in question is not fixed by sufficient clamping pressure. After the second material which has been folded around the sword is placed on the first material, the bend-over means is withdrawn back into its inactive starting position. When this occurs, it is unavoidable that at the insufficiently fixed places, the folded edges of the second material--particularly when it is very thin material, for instance formed of microfibers--are carried along (for example being rolled out). As a result, the properly folded second material workpiece is partially unfolded. In this way, an accurate seating of the second material on the first material cannot be obtained. This disadvantageous effect is further increased by possible wrinkling in the region of the insufficiently fixed folded edges of the folded second material.
German Utility Model No. 19 64 067 (corresponding to U.S. Pat. No. 3,528,378) discloses a machine for sewing pockets onto articles of clothing in which, on the lower side of a table part which is recessed in a table plate and can be raised and lowered, there are provided a plurality of fixing rams which are arranged spaced from each other. These rams can be extended in the vertical direction under the influence of pressure means and, in this connection, press upward from below, against the article of clothing, thereby fixing the previously folded, i.e., bent-over, edge regions of the pocket part between the article of clothing and the support plate, which acts as a "sword." Because of their spaced arrangement, it is not possible with these fixing rams to obtain a continuous, uninterrupted fixing of the folded edge regions over their entire length. In the case of the above-mentioned pockets with rounded edges, the folds that are always present in the corner regions prevent the previously folded edge regions of the bent-over pocket blank from being effectively fixed.
The prior art (DE 38 43 000 A1) also discloses a pressure hose which is relevant to the background of the invention. This publication discloses an annular clamping device, which is developed as a fold-free hose which can be acted on by pressure means, clamping a flat material in an embroidery frame.
The disclosures of all prior art materials mentioned herein are expressly incorporated by reference.